Compressor, in particular a radial piston compressor for carbon dioxide as a refrigerant

ABSTRACT

A compressor, in particular a radial piston compressor, further in particular a compressor for CO 2  as a refrigerant, including a compressor unit for compressing refrigerant and a drive shaft for driving the compressor unit and a motor chamber bounded substantially by a motor housing, wherein the motor chamber has a fluid connection to a suction gas side, in particular a suction gas chamber, of the compressor by means of a fluid connection formed at least partially in the drive shaft, wherein at least one device for accumulating oil is arranged in the fluid connection.

The present invention relates to a compressor, in particular a radialpiston compressor, more particularly a compressor for CO₂ asrefrigerant, as per the preamble of patent claim 1.

Compressors, in particular compressors for refrigerant such as forexample R134a, R404A, R507, R407c, R22 or R744 (CO₂), have becomeindispensible in this day and age and are used inter alia in the fieldof mobile cooling and air conditioning, such as for example theair-conditioning of passenger motor vehicles and utility vehicles, theair-conditioning of buses and trains and in-transit cooling, and also inthe static cooling of foodstuffs, in refrigerated warehouses or in thefield of medical technology. Such compressors are nowadays essentialalso in the field of air conditioning for buildings.

Examples of compressors which are used in some of the fields mentionedare known from the applicant's semi-hermetics catalog. In particular,reciprocating piston compressors having two, four, six and eightcylinders, which have swept volumes of approximately 62 cm³-3,215 cm³,are known from said catalog.

Furthermore, DE 103 56 373 A1 discloses a compressor in the form of aradial piston compressor which comprises a compressor unit forcompressing refrigerant and comprises a drive shaft for driving thecompressor unit. In the compressor according to DE 103 56 373 A1, thecentral points of the pistons are arranged in a common plane throughwhich the drive shaft extends perpendicularly, or to which a centralaxis extending in the longitudinal direction of the drive shaft isperpendicular.

Also known from the prior art are compressors, in particular radialpiston compressors, whose drive shaft is operatively connected to anelectric motor, the motor being delimited substantially by a motorhousing which in its interior defines a motor chamber, the motor chamberbeing fluidically connected via a bore in the drive shaft to a suctiongas chamber from which the refrigerant to be compressed is sucked. Tocool the motor, a partial mass flow of the suction gas from the suctiongas chamber is supplied to the motor chamber via a duct and is suppliedto the suction gas volume again via the abovementioned bore in the driveshaft. On account of the flow conditions, the partial mass flowconducted back to the suction gas volume contains oil. Said oil is usedfor lubricating bearings or the like. Depending on the operating stateof the compressor, however, a situation may arise (for example at lowrotational speeds) in which optimum lubrication does not take place.

Taking the prior art discussed above as a starting point, it is anobject of the present invention to specify a compressor in which goodlubrication is ensured for wide operating ranges.

Said object is achieved by means of a compressor having the features ofpatent claim 1, wherein further features and advantages of the inventionmay be gathered from the following description of the figures and fromthe subclaims.

The invention will be described by way of example below with referenceto the appended drawings on the basis of possible embodiments. In thedrawings:

FIG. 1 shows a first embodiment of a compressor according to theinvention in a partially sectional illustration in a horizontalinstallation situation;

FIG. 2 shows the embodiment as per FIG. 1 in a vertical installationsituation;

FIG. 3 shows a detailed illustration of a detail from FIGS. 1 and 2;

FIG. 4 shows a detailed illustration of a second possible embodiment ofa compressor according to the invention, similar to the illustration inFIG. 3; and

FIG. 5 shows a detailed illustration of a third possible embodiment of acompressor according to the invention, similar to the illustration inFIG. 3.

As can be seen for example from FIGS. 1 and 2, the first embodiment of acompressor 10 according to the invention has a compressor unit 12 and amotor unit 14. The motor unit 14 has a motor housing 16 which, in thefirst embodiment, delimits not only a motor chamber 18 but also, inpart, the compressor unit 12. Arranged in the motor chamber 18 inaddition to an electric motor is a drive shaft 22 via which the motor 20is operatively connected to the compressor unit 12. In the describedfirst embodiment, the compressor unit 12 has six pistons 24 which arearranged in the radial direction. The pistons 24 are arranged in acommon plane spanned by the piston longitudinal axes which extend in thepiston longitudinal direction, which plane is perpendicular to the driveshaft 22. It is pointed out at this juncture that a different number ofpistons 24 is self-evidently also conceivable, wherein the number ofpistons is determined in particular by the technical requirements of theuser of the compressor 10 (swept volume and desired compression power).

The compressor unit 12 is provided for the compression of refrigerants,wherein common refrigerants such as for example R134a, R404A, R507,R407c, R22 or preferably R744 (CO₂) are conceivable as refrigerant. Therefrigerant passes, on a suction gas side, via a suction gas chamber 26arranged at the suction gas side into cylinder bores 28 (which areformed in the radial direction) of the compressor 10, in which cylinderbores the pistons 24 are arranged in a reciprocating fashion. Thecompression of the refrigerant is realized by means of a movement of thepistons 24 in the radial direction. When the piston 24 has arrived in anupper position in the cylinder bore 28, that is to say the piston 24 hasarrived in a radially outwardly facing position, the refrigerant whichis then compressed is discharged into a compressed-gas chamber 30 whichis arranged at the high-pressure side and from which the compressedrefrigerant is provided to a refrigerant circuit assigned to thecompressor 10.

The compressor 10 also has, in addition to the compressor unit 12 andthe motor unit 14, an electrical terminal box 32 which is fastened tothe motor housing 16 of the compressor 10 by means of fastening elementsfor example in the form of screws. The stator of the electric motor 20is positioned in the motor housing 16 and may be fixed to the latter forexample by means of screws.

The electrical terminals for the compressor 10, in particular theterminals for the current or voltage supply to the electric motor 20,are arranged in the terminal box 32. Also contained in the terminal box32 are electronic motor protection components to which components suchas for example a heat protection thermostat 38 can also be connected.For a supply of electricity, the terminal box 32 has a plurality ofcable inlets 36 which, as illustrated in FIG. 1, may be closed off whennot being used, for example by means of closure elements. The cableinlets 36 illustrated are preferably pre-punched, originally closedcutouts which are first opened by being pushed in. Therefore, noseparate components are required; these are rather regions of the outercontour of the terminal box 32 which have been pre-punched such thatthey can be opened more easily.

On account of the high pressures of the refrigerant (for example CO₂), aheat protection thermostat 38 is preferably not arranged so as to be indirect contact with the refrigerant but rather arranged in the motorhousing 16 so as to be separate from the refrigerant. In this way, theheat protection thermostat 38 has only an indirect thermal connection tothe refrigerant. The heat protection thermostat 38 may be connected toelements in the terminal box 32 by means of a cable 39, for examplethrough a cable inlet 36.

For the lubrication of the compressor 10, lubricant in the form of oil41 is situated in the compressor 10. The oil 41 is stored in the motorchamber 18, wherein the oil 41 is used not only for lubricating parts ofthe compressor 10 arranged in the motor chamber 18 but rather also forlubricating parts of the compressor 10 arranged outside the motorchamber 18. In the region of the motor chamber 18, it is necessary tolubricate bearings 40, 42, 44 (front bearing bush 42, rear bearing bush44 and bearing 40 for mounting the drive shaft 22 in the motor housing16). Outside the motor chamber 18, the movable parts of the compressorunit 12, in particular the pistons 24, require correspondinglubrication.

The compressor 10 has a fluid connection 45 between the motor chamber 18and the suction gas side (suction gas chamber 26), which fluidconnection, aside from returning the partial mass flow which cools themotor, also serves for the lubrication of the bearings 40, 42, 44. Thefluid connection 45 is formed to a large extent in the drive shaft 22and consists inter alia of an axial cutout formed in the drive shaft 22in the manner of a bore 46 extending in the axial direction.Furthermore, the fluid connection 45 comprises four radial cutoutsarranged in the radial direction in the drive shaft 22, said radialcutouts taking the form of a first, a second, a third and a fourthradial bore 48, 50, 52, 54 which are fluidically connected to the bore46. The first radial bore 48, which extends through the entire driveshaft 22 so as to have two openings to the motor chamber 18, serves forreceiving the partial mass flow which also contains oil or oil mist. Thesecond, third and fourth radial bores 50, 52, 54 are provided for thelubrication of the bearings 40, 42, 44. Oil 41 can emerge through saidbores in the radial direction into the bearing points to be lubricated.The outflow of the oil 41 in the radial direction is assisted by therotational movement of the drive shaft 22 and the resulting centrifugalforces generated.

To permit cooling of the motor, the suction gas chamber 26, as alreadymentioned above, is connected to the motor chamber 18 by means of afluid connection 45. The fluid connection 45 has inter alia the firstradial bore 48, which serves as an inlet for the partial mass flow, andthe bore 46 which is fluidically connected to said first radial bore.For the lubrication of the bearing 44 (second bearing bush), the fluidconnection also has a radial bore 54 which is fluidically connected tothe bore 46. The radial bore 54 is fluidically connected to a secondaxial cutout in the form of a second bore 56 which extends in the axialdirection in the drive shaft 22, which second bore has a cross sectionsmaller than the cross section of the bore 46 and which second bore isfluidically connected, at its end facing away from the motor chamber 18,to the suction gas chamber 26. Arranged at the suction-gas-side end ofthe bore 56 is a point of reduced cross section in the form of a nozzle58 which limits and defines the inflow of oil into the suction gaschamber 26. According to requirements, the nozzle 58 is selected at thefactory and the corresponding cross section or the correspondingthroughflow rate is adapted to the design requirements.

It is additionally possible, in alternative embodiments of theinvention, for the oil inflow to be regulated by means of the bore crosssection of the radial bore 54 or of the axial bore 56, for example bymeans of the bore cross section itself or by means of a constrictionarranged in the bore 54 or 56, or an orifice or a flap, in addition tothe nozzle 58 or instead of the nozzle 58. The orifice or flap may bedesigned so as to be non-adjustable or adjustable, such that by meansthereof, the oil flow or the lubrication via the suction gas chamber 26can be controlled or regulated as a function of external parameters andif appropriate also as a function of parameters of the compressoritself. Furthermore, it is possible for the nozzle 58 to be providedwith a variable nozzle cross section and/or an upstream valve whichopens or closes on a predetermined or variable clock cycle such that theoil quantity supplied to the suction gas chamber 26 can be regulated orcontrolled.

The two axial cutouts 46 and 56 are formed in the drive shaft 22preferably axially parallel to one another with a radial spacing, andpreferably in the manner of axially parallel bores.

To ensure a reliable supply of oil in particular to the bearings 42, 44,a device for causing a build-up of oil, in the form of a tubular elementor tube 60, is arranged in the fluid connection 45, which device servesto ensure that sufficient oil 41 is supplied to the nozzle 58 and to theradial bores 52, 54. Aside from the function of causing a build-up, thetube 60, on account of its being fluidically connected, at its sidefacing away from the motor chamber, to the suction gas volume, serves toensure the return of the partial mass flow from the motor into thesuction gas chamber. An oil overflow device in the form of a tube 61which is pressed into the drive shaft 22 and which extends into theaxial bore 46 serves for the discharge of excess built-up oil 41. Itshould however be noted that the tube 60 is provided not for thelubrication of the compressor unit 12 but rather merely as an oiloverflow in the event that too large an oil quantity has built up. Thedevice for causing a build-up of oil, in the form of the tube 60, isdesigned to cause a build-up of oil 41 while maintaining anuninterrupted fluid connection. It should be noted that the tube 60 hasan outer diameter smaller than the diameter of the axial bore 46, andthat the tube 60 is arranged concentrically with respect to the axialbore 46 and projects into the latter. As an alternative to this, anon-concentric, parallel arrangement with respect to the bore is alsoconceivable.

The compressor 10 illustrated in FIG. 1 is illustrated in a verticalinstallation situation in FIG. 2, wherein in this installationsituation, the lubricant in the form of the oil 41 covers the radialcutout (radial bore 48). Operation is possible even with a coveredradial cutout, wherein it would also be conceivable for the radial bore48 to be arranged above the oil level, such that again, oil mist ratherthan oil 41 is sucked in.

Additionally or alternatively to the tube 60 as a device for causing abuild-up of oil, it is also conceivable for an orifice 62 (in thisregard cf.

FIG. 4) arranged for example in the drive shaft 22, and/orreservoir-like or basin-like cutouts 64 (in this regard, cf. FIG. 5)which extend in the radial direction, to be provided in the fluidconnection 45 between the motor chamber 18 and the suction gas side orsuction gas chamber 26 in order to cause a build-up of oil 41. Asillustrated in FIG. 5, the reservoir-like cutouts 64 are formed in theregion of the radial bores 52, 54. It is self-evidently also conceivablefor reservoir-like cutouts of said type to also be provided in theregion of the further cutouts/bores arranged in the radial direction inthe drive shaft. The centrifugal forces arising as the drive shaft 22rotates ensure a reliable supply of oil to the cutouts 64.

Even though the invention has been described on the basis of embodimentswith a certain combination of features, the invention however alsoencompasses further combinations as specified in particular but notexhaustively by the subclaims.

1. A compressor, in particular radial piston compressor, moreparticularly a compressor for CO₂ as refrigerant, which compressorcomprises a compressor unit for compressing refrigerant and comprises adrive shaft for driving the compressor unit and also comprises a motorchamber delimited substantially by a motor housing, the motor chamberbeing fluidically connected to a suction gas side, in particular suctiongas chamber, of the compressor via at least one fluid connection formedat least partially in the drive shaft, wherein at least one device forcausing a build-up of oil is arranged in the fluid connection.
 2. Thecompressor as claimed in claim 1, wherein the at least one device forcausing a build-up of oil is formed so as to maintain an uninterruptedfluid connection.
 3. The compressor as claimed in claim 1, wherein thefluid connection comprises an in particular cylindrical first axialcutout which is formed in the axial direction in the drive shaft.
 4. Thecompressor as claimed in claim 1, wherein the fluid connection isfluidically connected to at least one in particular cylindrical radialcutout which is formed in the radial direction in the drive shaft. 5.The compressor as claimed in claim 3, wherein the fluid connection has atubular element whose outer diameter is smaller than the diameter of theaxial cutout, wherein the tubular element is arranged parallel to orconcentrically with respect to the axial cutout and projects at leastpartially into the latter.
 6. The compressor as claimed in claim 5,wherein the tubular element is fluidically connected to the suction gasside, in particular suction gas chamber.
 7. The compressor as claimed inclaim 3, wherein the fluidic connection comprises a second, inparticular cylindrical axial cutout which is formed in the axialdirection in the drive shaft and whose cross section, in particulardiameter, is smaller than that of the first axial cutout, and in thatthe second axial cutout is fluidically connected at one end thereof tothe first axial cutout and which opens out at its second end into thesuction gas side.
 8. The compressor as claimed in claim 7, wherein thesecond axial cutout is fluidically connected at one end thereof to thefirst axial cutout by means of at least one radial cutout, preferablyradial bore, which extends radially relative to said first axial cutout.9. The compressor as claimed in claim 1, wherein the fluid connectionhas a point of reduced cross section.
 10. The compressor as claimed inclaim 9, wherein the point of reduced cross section comprises a nozzleor an orifice or a point of reduced material cutout or a flap.
 11. Thecompressor as claimed in claim 9, wherein the point of reduced crosssection is arranged in the second axial cutout and/or in the radialcutout.
 12. The compressor as claimed in claim 9, wherein the point ofreduced cross section has an adjustable, in particular controllable orregulable cross section.
 13. The compressor as claimed in claim 1,wherein the fluid connection comprises at least one further inparticular reservoir-like or basin-like cutout which is arranged in thedrive shaft and which is designed to cause a build-up of the oil. 14.The compressor as claimed in claim 1, wherein an oil overflow isprovided which determines the amount of oil built up or accumulated. 15.The compressor as claimed in claim 14, wherein the oil overflowcomprises a tubular element which is arranged in a radial cutout in thedrive shaft and which projects into the fluid connection between themotor chamber and the suction gas side.